1. Field of the Invention
This invention relates to supporting each exciter winding bar in the end winding region of a dynamoelectric machine so as to permit a certain degree of axial expansion as the exciter winding bar extends from one end of the stator slot, while at the same time securing the exciter winding bar against radial and circumferential motion.
2. Description of the Prior Art
Y. S. Hargett, in "Large Steam Turbine-Driven Generators", published by General Electric Company; Schenectady, N. Y., December 1978, provides a comprehensive description of dynamoelectric machines used in the production of electrical power. An end view of liquid-cooled generator windings is shown on Page 22 of the reference. For proper operation of the turbine-generator, certain auxiliary equipment is required, and one of the major items is an excitation system which functions to provide magnetizing power to the rotating generator field winding.
New designs for static excitation systems have been developed to displace the time-proven shaft-driven rotating exciters. For example, the GENERREX excitation system developed by General Electric Company, is intregral within the generator itself, and is described by G. M. Cotzas et al, "Description and Tests of the GENERREX Excitation System for Large Steam-Turbine Generators", IEEE Trans., Vol. PAS-95, No. 3, May/June 1976, pp. 803-810. The GENERREX-CPS (Compound Power Source) excitation system utilizes generator voltage and current, and was developed to meet the demand for both high initial response and high response ratio performance characteristics. Thus, excitation system response ratios of 3.5 have been supplied.
Although a definite trend is observed in recent years toward higher performance levels, significant interest remains for the based level of 0.5 response. The GENERREX-PPS (Potential Power Source) excitation system, incorporating a potential power source integral to the generator, was developed to meet this demand. It has been described in a paper by G. M. Cotzas et al, "GENERREX-PPS(Potential Power Source) Excitation System for Wisconsin Power & Light, Edgewater 5", presented at the Forty-Third Annual American Power Conference, Chicago, Ill., Apr. 27-29, 1981. The concept of GENERREX-PPS excitation system retains many desirable features of the GENERREX-CPS system. Accordingly, compact arrangement of equipment is provided for reduced space requirements and simplified maintainability of the generator. Control of generator field voltage is by means of direct high-speed thyristor action. The excitation potential source consists of a winding made up of three exciter winding bars or potential bars (each hereinafter referred to as a "P" bar) placed in the upper part of three selected stator winding slots in the stator core. An improved support system for securing the "P" bars of the excitation system in the slots of the stator core, in such a manner as to be able to withstand the operating conditions of the dynamoelectric machine and to avoid stresses caused under sudden short circuit conditions, is disclosed in the copending application of Butman, Jr. et al, U.S. Ser. No. 302,962, coassigned and filed concurrently herewith, and is incorporated herein by reference.
In the end winding region beyond the stator slots, a different form of support is required. A tying arrangement, for securing the armature bars (also referred to as stator bars) in the end portions of the stator winding, is shown in U.S. Pat. No. 3,437,859 issued Apr. 8, 1969 to E. E. Gibbs et al. In that patent, particularly in FIG. 8, there are shown circumferential hoops disposed at an angle with respect to the armature bars to provide support of the skewed end windings of the armature bars. The hoops in the patent to Gibbs et al, are attached to the armature bars by means of ties which are more particularly described in U.S. Pat. No. 3,566,010 issued Feb. 23, 1971 to Karl F. Drexler et al. In particular, the ties are formed by wrapping with strands of high tensile strength material impregnated with a curable resin. The strands are wound under tension about the portions which are to be affixed and the resin is subsequently cured to a rigid state. This tying process is generally referred to as "wrapping" and is hereinafter referred to as such. Other structures for retaining generator end windings are shown in the U.S. Pat. No. 3,135,888 issued June 2, 1964 to A. D. Coggeshall. The three patents cited above are incorporated herein by reference as background material for the present invention.
Prior art designs of dynamoelectric machines, while adequate for their intended purpose, do not provide restraints for the "P" bar against high radial and circumferential movement which may now arise in the GENERREX-PPS system due to excessive lateral forces such as are possible under electrical fault conditions. Nonetheless, the support system for such windings must be capable of allowing a certain amount of axial motion which arises primarily because of thermal expansion forces.
It is therefore an object of the present invention to provide an end winding support system for the "P" bars of the excitation system of a dynamoelectric machine.
It is a still further object of the present invention to provide an end winding support system for the "P" bars which permits a certain amount of axial expansion, while at the same time securing the windings against both circumferential and radial forces.